Pruning 14 reseller paths to one direct seller cut CPMs 22%

Pruning 14 reseller paths to one direct seller cut CPMs 22%

A mid-market DSP buyer was reaching the same publisher inventory through 14 distinct supply paths. Supply path optimization (SPO = choosing the cleanest, cheapest route to a given impression) restructured this.

1. They pulled log-level data and grouped bid requests by the publisher domain plus the seller account ID in the sellers.json file.
— 14 paths resolved to one publisher: 1 direct, 13 reseller hops.
2. They measured win rate and median clearing price per path for identical audience segments.
— The direct path cleared at a $3.10 median; reseller paths averaged $3.98 for the same user.
3. They blocklisted 11 of the 13 reseller paths in the DSP, keeping two as failover.

Evidence: over 30 days, blended CPM dropped from $3.84 to $2.99, a 22% reduction, while won impressions on that publisher fell only 4%. The duplicate requests had been bidding against each other, inflating the second-price floor.

Why it matters: paths to the same impression are not interchangeable. Reseller hops add a margin and frequently re-auction inventory you already had a direct line to. Deduplicating by seller ID, not by domain, is where the saving lives.